LDO catalysts

A very early patent in the 1970s (518,519) on the application of LDHs concerned the reduction of nitrobenzene into aniline. Brocker et al. prepared CoMnAl-LDH catalysts from the corresponding LDHs and obtained a 66% yield of aniline at 150°C and 133 atm. Actually, many LDO catalysts are found to promote the reduction of aromatic nitro compounds to anilines (350,520,521). For instance, Kumbhar et al. (350,520) found that calcined MgFe-LDHs are very efficient catalysts for the reduction of 4-nitrotoluene to 4-aminotoluene at 100% selectivity. They noted that these catalysts are also effective for the hydrogenation reduction of various other aromatic nitro compounds. 

Fritz et al. used Pt-Sn-LDH-derived LDO catalysts in the dehydrogenation of C2-C10 alkanes (523). Li et al. investigated similar Pt/MgAl-LDO and PtSn/... 

Another example is the synthesis of 2-ethyl-2-hexenal from the condensation of n-butyraldehyde over MgAl-COs-LDO catalysts. At lower than 200°C, the reaction occurs at close to 75% conversion with more than 80% selectivity. 

There have been many other investigations of the applications of LDO catalysts to Claisen-Schmidt condensation (540). For example, with activated MgAl-COs-LDH as catalyst, benezaldehyde and 2-hydroxylacetophenone react at 50°C to give the desired compounds (2-hydroxychalcone and flavanone) at 80% conversion and 78% selectivity (541). As another example, the condensation of citral and acetone produces an intermediate that can be finally transformed to chemically useful ionones (542,543). The use of calcined LDH results in 70% selectivity at about 95% conversion. In addition, Dumitriu et al. (544) and Suzuki... 

The methylation of aniline with methanol over calcined MgAl-LDHs results in an almost single product, i.e., A-methylaniline, in up to 68% yield. LDHO catalysts are more active than mixed Mg0-Al203 (562). Aniline can also be methylated to the same product, with dimethylaniline as a minor product, using dimethyl carbonate over an MgAl-LDO catalyst at 275°C (556). Anotha- example is the LDO-catalyzed alkenylation of formamide with vinyl formate to give N-vinylformamide. The intamediate A-vinylformamide can then be polymoized into poly(A-vinylformamide), which can be converted into polyvinylamine by hydrolysis (563). 

The reaction of ethylene oxide with n-butanol gives 2-butoxyethanol (527,578) in very high yield over MgAl- and CuCr-LDO catalysts. Epoxides, such as propylene oxide and styrene oxide, can also react with CO2 to form cyclic carbonates with MgAl-oxide catalysts (579). On the industrial scale, ethylene oxide and propylene oxide can be polymerized into water-soluble polyols over an MgAl-COs-LDO catalyst (580-583). 

As described previously, acetone can be transferred to a,p-unsaturated ketone (mesityl oxide) by condensation and then hydrogenated to methyl isobutyl ketone over NiMgAl-LDO catalysts (536a). The same reaction can be accomplished in one step over Pd supported on MgAl-LDO (586,587). 

Synthesis gas (CO + H2) can be obtained cheaply from coal, oil, or natural gas and is a key material in some routes to bulk organic compounds, such as methanol, acetic acid, alcohols, and hydrocarbons. LDO catalysts have been intensively explored in both the production and the use of this material. 

Under the proper conditions, alkylene oxides can react with other chemicals by ring opening over LDH-derived catalysts. For example, the hydration of ethylene oxide over NiAl-VOs -LDO catalyst at 150°C produces glycol in 95% yield (576,577). 

ZnCr- and CuZnAl-LDOs. LDO catalysts generally give rise to high selectivity for methanol, while surface doping with Cs on mixed oxides increases catalyst stability (162,610-612). Higher alcohols can be also obtained with similar catalysts but at higher temperature and with a lower CO/H2 ratio (610,611). The doping of alkali, such as Cs, promotes the formation of branched alcohols (613). In addition, Ru supported on LDH-derived oxides, exhibits substantial selectivity toward alcohols, mainly methanol, at moderately low pressures (614). 

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